The present invention relates to an improvement in the production of linear .alpha.-olefins. More particularly, the present invention relates to an improvement in the method for the production of linear .alpha.-olefins useful as a comonomer for modifying polyolefins or as a starting material for the manufacture of plasticizers, surface active agents and the like by using a catalyst having a high activity and excellent stability, in which the product can be obtained in a high purity and with an optimum distribution of the respective .alpha.-olefin compounds relative to the increased yields of the most useful .alpha.-olefin compounds having 6 to 18 carbon atoms in a molecule.
As is well known, linear .alpha.-olefins are useful, for example, as a comonomer for the modification of polyolefins or as a starting material for the manufacture of plasticizers, surface active agents and the like. In this regard, linear .alpha.-olefin compounds having 6 to 18 carbon atoms are particularly useful and widely used in large quantities.
These linear .alpha.-olefin compounds are prepared usually by the catalytic oligomerization of ethylene in the presence of a so-called Ziegler-type catalyst. Various types of catalysts are known to be suitable for the purpose including, for example, a binary catalyst system comprising an ethyl aluminum chloride as combined with titanium tetrachloride as the transition metal compound, optionally, with further admixture of a third ingredient with an object to enhance the selectivity.
The above mentioned catalyst systems using a titanium compound are not quite satisfactory in respect of the activity and selectivity of the catalyst.
On the other hand, several catalyst systems for the production of linear .alpha.-olefins have been proposed in which a zirconium compound is used as the transition metal compound (see, for example, Japanese patent Kokai 58-109428, 58-113138 and 58-201729).
Although the catalytic activity of these catalyst systems using a zirconium compound is higher than that of the above mentioned catalyst systems using a titanium compound, they have some problems and disadvantages that waxy materials as a by-product are produced in a very large amount (see Japanese patent Kokai 58-109428 and 58-113138) and that the oligomers having 4 carbon atoms in a molecule are produced in an extremely high yield and the purity of the linear .alpha.-olefin product is relatively low (see Japanese patent Kokai 58-201729).